For many industrial applications, it is desirable to have a low cost high voltage DC power supply. One such application, for example, is the use of high voltage DC in electrostatic precipitators for pollution control. To obtain such high voltage DC power a step-up transformer connected to commercial power lines and a rectifier connected to the output of the transformer can be used. The high voltage output of the transformer may vary from about 10 KV to several hundred KV depending upon the application. Because of the magnitude of such voltage a high voltage clearance space must be provided around the terminals of all such devices.
Because of the high voltage present inside high voltage transformers and rectifiers and to enhance cooling of such devices, it is common to immerse these devices in an insulating liquid such as oil. Such oil immersed devices are contained in metal housings having the high voltage connections brought to the exterior of the metal, conductive, housing by means of a set of high voltage bushings. These bushings are brought out of the tank in a spaced relationship to provide adequate high voltage clearance between bushings. When a separate transformer and high voltage rectifier are used to form a DC power supply, adequate high voltage clearance must be provided for the terminals of both devices. U.S. Pat. No. 3,805,140 is an example of a separate oil filled rectifier and required insulation. In many applications the additional space required is not available or increases the installation cost.